Portable electronic devices, such as smartphones and tablet computers, can be exposed to liquid or moisture during their normal use. For example, such devices may be exposed to rain, or sweat or an accidental liquid spill. Additionally, in some instances the devices may be waterproof or highly water resistant in which case a user may knowingly expose the device to water when swimming or to wash the device.
Many portable electronic devices include a receptacle connector that has an opening or port at an exterior of the device in which multiple contacts reside. A corresponding plug connector can be inserted into the receptacle connector port to charge the internal battery of the device, to transfer data between the device and a second device, or for audio or video input or output, among other functions. If the contacts within the connector port are exposed to liquid while a voltage is applied to one or more of the contacts a short circuit could damage the connector or electronic device. Additionally, ions and other solids or materials within the liquid can react with the electrical contacts causing corrosion and other damage.
Some electronic devices include a liquid contact sensing circuit within the device that takes measurements, such as resistance and capacitance measurements, across one or more of the electrical contacts of the device in order to detect the presence of liquid on those contacts. In response to detecting the presence of liquid corrective actions can be taken in real time. For example, the electronic device can power down certain sensitive electronic components within the device. Alternatively, or additionally, the electronic device can reduce or terminate power supplied to its connector such that the voltage across electrical contacts of the connector is reduced or dropped to zero in response to having detected the presence of short-circuit or corrosion causing moisture within the port.
While terminating or reducing power supplied to a connector can prevent damage to the electronic device and/or connector, it can also cause user frustration if the liquid sensing circuit incorrectly determines that a harmful liquid is present on the contacts. For example, not all liquid is likely to result in contact corrosion. Some liquids that have minimal or no dissolved materials within them are not a serious concern for likely contact corrosion. Similarly, the liquid sensing circuit might incorrectly determine that solid material (e.g., dirt, dust, grease, etc.) that is present on one or more of the contacts is a harmful liquid and act accordingly even though the solid material does not present a safety or corrosion concern.
Thus, despite the existence of various known liquid detection methods and circuits, new and improved methods for detecting liquid at a connector of a portable electronic device and distinguishing potentially harmful liquids from other contaminants are desirable.